1. Field of the Invention
The present invention relates to a layered double hydroxide oriented membrane and a method for producing the same.
2. Description of the Related Art
Layered double hydroxides (hereinafter also referred to as LDHs) represented by hydrotalcite are a group of substances having exchangeable anions between hydroxide layers and are used as, for example, catalysts and adsorbents, as well as dispersing agents in polymers for improving heat resistance, by taking advantage of their characteristics. In particular, LDHs have been attracting attention in recent years as materials that conduct hydroxide ions, and addition to the electrolyte of an alkaline fuel cell and the catalyst layer of a zinc-air battery has been also investigated.
In light of conventional areas of application such as catalysts, a large specific surface area is required, and it is therefore sufficient to synthesize and use LDHs in a powder form. On the other hand, in light of application to an electrolyte that takes advantage of hydroxide ion conductivity in alkaline fuel cells or the like, highly dense LDH membranes are desired for preventing mixing of fuel gas and obtaining a sufficient electromotive force.
Patent Documents 1 and 2 and Non-Patent Document 1 disclose oriented LDH membranes, and the oriented LDH membranes are prepared by horizontally suspending a surface-sulfonated polymer substrate in a solution containing urea and metal salts to cause LDHs to nucleate and grow in an oriented manner. An intense peak of the (003) plane is observed in all X-ray diffraction results of the oriented LDH thin membranes obtained in these documents.